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3 CAPA 7 & 8 A scuba tank has a volume of 3900 cm 3. For very deep dives, the tank is filled with 50% (by volume) pure oxygen and 50% pure helium. 8. How many helium molecules are there in the tank if it is filled at 20°C to a gauge pressure of 12.5 atm? PV = NkT The same number as there are oxygen molecules. N = 6.60 x 10 23

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4 Kinetic Theory of Gasses 1. Gases contain a large number of molecules moving in random directions with a variety of speeds. 2. Molecules are very far apart and don’t exert forces on one another except when they collide. 3. Molecules obey Newton’s Laws. 4. Collisions are perfectly elastic.

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7 CAPA 9 & 10 A scuba tank has a volume of 3900 cm 3. For very deep dives, the tank is filled with 50% (by volume) pure oxygen and 50% pure helium. 9. What is the ratio of the average kinetic energies of the two types of molecules? KE = 3/2 kT (for each molecule) Since the gases are at the same temperatures they have the same kinetic energies. Ratio = 1.0